<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <input type="text" class="username"> 
    <br>
    <input type="text" class="pwd">
    <br>

    <script src="../js/reg.js"></script>

    <script>

        const oUser = document.querySelector('.username') ;

        oUser.onblur = function() {
            const username = this.value ;
            if(userTestFn(username)) {
                alert('正确')
            } else {
                alert('错误')
            }
        }

    </script>
    
</body>
</html>